1. Field of the Invention
This invention pertains to an image processing apparatus and printing apparatus that record images by using a recording material.
2. Description of the Related Art
Heretofore there have been many instances in which dyes stably dissolved in water as the main component have been used as the coloring material in the ink which has water as the principal component used in inkjet printing apparatus. Because the molecules in these dyes absorb light one by one, the colors become brighter. Further, because of permeation into and adsorption onto the receiving layers of special printing media, the surface properties of the printing media maintain their coloring intact. However, the color material in the dye ink (dye-based ink) exists in molecular form. As a result, there are the problems that the color material in the dye-based ink easily migrates in the printing medium after printing, color fixing is slow and because of light or gas it is easy for it to break down and color degradation occurs easily.
In recent years the necessity for improving the color fixing directly after printing and ameliorating the resistance characteristics of environmental adverse affect or waterproofing properties of the printing materials has increased. In order to respond to this, inkjet printing apparatus using ink that utilizes pigments in the color material (pigment-based ink) have been developed. Because the color material in pigment-based ink exists as particles, the color material is slow to migrate in the printing medium after printing and the color fixing is fast. Additionally, even if the molecules on the surface of the color material granules break down due to light or gas, because the molecules inside them contribute to the color fixing, color degradation occurs with difficulty.
However, especially when printing with pigment-based ink, the phenomenon sometimes occurs in which the color of regular reflected light reflected onto the printing components differs from the color of the original lighting and the color of the ink used in the printing. This phenomenon is called the “bronze phenomenon”. This “bronze” phenomenon in particular noticeably occurs when printing on a printing medium that has a high gloss.
This bronze phenomenon can be quantitatively measured. For example, using a three dimensional Gonio-spectrophotometric Color Measurement System (GCMS-4) from Murakami Color Research Laboratory, it is possible to measure the color of regular reflected light with respect to a single color patch printed with pigment-based ink on glossy paper by irradiating with light from a 45° direction and receiving it at an opposite 45° position.
FIG. 22 is a diagram showing this measuring system in typical form. In FIG. 22, B0001 indicates the illumination means by which the printing medium B0003, the object of evaluation, is illuminated. B0002 indicates the photodetecting means by which the reflected light from B0003, the object of evaluation, is detected. The photodetecting means B0002 is positioned inclined to the same angleψ as the illumination means on the opposite side with respect to the normal line direction of the printing medium B0003, that is, it is placed in the normal reflection direction. B0004 indicates the fixed base to which the printing medium B0003 is affixed on which the targeted patch which is the evaluation target is printed. B0005 indicates the measuring site that the photodetecting means B0002 will measure. B0006 indicates the light shielding means that screens out light from outside.
Next, an explanation of the method for calculating the bronze characteristics from the measured regular reflected light of the printing medium will be given. The tristimulus values XXYYXZ are calculated from the spectral intensityRX(λ)  [Number 1]
according to the following equation (1) of the regular reflected light from the printing medium B0003 measured by the photodetecting means B002
                    [                  Number          ⁢                                          ⁢          2                ]                                                                      Xx          =                                    ∫              380              780                        ⁢                                          Rx                ⁡                                  (                  λ                  )                                            ⁢                                                          ⁢                                                x                  _                                ⁡                                  (                  λ                  )                                            ⁢                              ⅆ                λ                                                    ⁢                                  ⁢                  Yx          =                                    ∫              380              780                        ⁢                                          Rx                ⁡                                  (                  λ                  )                                            ⁢                                                y                  _                                ⁡                                  (                  λ                  )                                            ⁢                                                          ⁢                              ⅆ                λ                                                    ⁢                                  ⁢                  Zx          -                                    ∫              380              780                        ⁢                                          Rx                ⁡                                  (                  λ                  )                                            ⁢                                                z                  _                                ⁡                                  (                  λ                  )                                            ⁢                              ⅆ                λ                                                                        (        1        )            
However, when measuring the regular reflected light with the optical system of FIG. 22 with equation (1) above, because of the high degree of gloss on glossy paper, the range of the measured values of the regular reflected light approach the measurements of the light source. That is to say, it is similar to the measuring system in which the light from the light source is directly measured. Accordingly, unlike calculation of the tristimulus values of the color of the object from normal reflection, the spectral intensity of the regular reflected light is considered as the relative spectral distribution of the light source and obeys the calculation method for the tristimulus values of the light-source color. x(λ), y(λ), z(λ)  [Number 3]of equation (1) are the color matching functions of JISZ8782. Also, normalization by multiplication of the proportional constant is not performed here but normalization by multiplying with
                    [                  Number          ⁢                                          ⁢          4                ]                                                            K        =                  100                                    ∫              380              780                        ⁢                                                            y                  _                                ⁡                                  (                  λ                  )                                            ⁢                              ⅆ                λ                                                                        (        2        )            may be performed.
With the white board of the perfectly diffused reflector as the measurement target, from the spectral intensityS(λ)  [Number 5]of the illuminator B0001 measured by measuring the spectral intensity of its regular reflected light with B0002, the illumination tristimulus values XS, YS and ZS are calculated from equation (3) below. Equation (3) is based on the calculation method for the tristimulus values of the light-source color and is a conversion equation that calculates the tristimulus values XS, YS and ZS from the spectral data of the above-mentioned illumination.
                    [                  Number          ⁢                                          ⁢          6                ]                                                                      Xs          =                      k            ⁢                                          ∫                380                780                            ⁢                                                S                  ⁡                                      (                    λ                    )                                                  ⁢                                                      x                    _                                    ⁡                                      (                    λ                    )                                                  ⁢                                  ⅆ                  λ                                                                    ⁢                                  ⁢                  Ys          =                      k            ⁢                                          ∫                380                780                            ⁢                                                S                  ⁡                                      (                    λ                    )                                                  ⁢                                                      y                    _                                    ⁡                                      (                    λ                    )                                                  ⁢                                  ⅆ                  λ                                                                    ⁢                                  ⁢                  Zs          =                      k            ⁢                                          ∫                380                780                            ⁢                                                S                  ⁡                                      (                    λ                    )                                                  ⁢                                                      z                    _                                    ⁡                                      (                    λ                    )                                                  ⁢                                  ⅆ                  λ                                                                                        (        3        )            The x(λ), y(λ), z(λ)  [Number 7]of equation (3) are the color matching functions of JISZ8782. Additionally, the k of equation (3) is the proportional constant and the value of YS of the tristimulus value is determined so as to agree with the photometric quantity.
Next, the regular reflected light L*a*b* values of B0003 based on JIS Z8729 are calculated from the tristimulus values XX, YX and ZX of the regular reflected light of the printing medium B0003, which is the evaluation targets detected by B0002, and the tristimulus values XS, YS and ZS of the illuminator B0001. In this regard, the tristimulus values (XX, YX and ZX) of the regular reflected light of B0003 are used in the values of X, Y and Z, and the tristimulus values (XS, YS and ZX) of the light source are used in the values of Xn, Yn and Zn in equations (1) through (4) of JIS Z8729. That is, the a* and b* values are calculated by equation (4) below.
                    [                  Number          ⁢                                          ⁢          8                ]                                                                                  a            *                    =                      500            ⁡                          [                                                f                  ⁡                                      (                                          Xx                      Xs                                        )                                                  -                                  f                  ⁡                                      (                                          Yx                      Ys                                        )                                                              ]                                      ⁢                                  ⁢                              b            *                    =                      200            ⁡                          [                                                f                  ⁡                                      (                                          Yx                      Ys                                        )                                                  -                                  f                  ⁡                                      (                                          Zx                      Zs                                        )                                                              ]                                                                      Here,
                    When        ⁢                                  ⁢                  Xx          Xs                    >      0.008856        ,                  ⁢                  f        ⁡                  (                      Xx            Xs                    )                    =                        (                      Xx            Xs                    )                          3          _                                        When        ⁢                                  ⁢                  Xx          Xs                    ≤      0.008856        ,                  ⁢                  f        ⁡                  (                      Xx            Xs                    )                    =                        7.78          ⁢                      Xx            Xs                          +                  16          116                                        When        ⁢                                  ⁢                  Yx          Ys                    >      0.008856        ,                  ⁢                  f        ⁡                  (                      Yx            Ys                    )                    =                        (                      Yx            Ys                    )                          1          3                                        When        ⁢                                  ⁢                  Yx          Ys                    ≤      0.008856        ,                  ⁢                  f        ⁡                  (                      Yx            Ys                    )                    =                        7.78          ⁢                      Yx            Ys                          +                  16          116                                        When        ⁢                                  ⁢                  Zx          Zs                    >      0.008856        ,                  ⁢                  f        ⁡                  (                      Zx            Zs                    )                    =                        (                      Zx            Zs                    )                          1          3                                        When        ⁢                                  ⁢                  Zx          Zs                    ≤      0.008856        ,                  ⁢                  f        ⁡                  (                      Zx            Zs                    )                    =                        7.78          ⁢                      Zx            Zs                          +                  16          116                    (4)
Because the bronze is related not to the brightness of the image of the reflected illumination but to its color, the L* values which indicate brightness are not used for evaluation. In this detailed statement only the a*b* values in the CIELab color space are used in evaluation of the bronze characteristics.
FIG. 23 shows the bronze characteristics of various pigment-based inks and displays the measured results of 9 appropriately possible pigment-based inks for this invention in a*b* values. Various single colored patches on which various pigment-based inks of cyan, magenta, yellow, second black, light cyan, light magenta, red, green and gray were printed were measured by the measuring system for the regular reflected light mentioned above and the a*b* values were calculated from the above equation with the measured results. It is also a figure in which the a*b* values calculated in the above manner are plotted on an a*b* plane. In FIG. 23 the origin expresses the light-source color. Furthermore, the lines extending from the origin indicate by way of example the lines for the yellow, red and green hues in the color gamuts from the above-described measuring system. Additionally, as will be explained in an embodiment described hereafter, first black is used in highly concentrated regions and is an ink seldom added to other inks at the same pixel and is not shown in FIG. 23. The bronze characteristics are expressed by the a*b* values which signify the colors of the regular reflected light (hue·saturation).
As shown in FIG. 23, the reflected light of the cyan ink printed patch, for example, is observed as having a tinged with red to it. Moreover, this red is observed as a vivid red because of the large distance from the origin. Also, the reflected light of the second black patch is observed as a color tinged with yellow. Thus, the bronze phenomenon is a phenomenon in which the color measured by the system for regular reflected light differs both from the color of the original illuminated light and the color of the ink itself.
Ink manufacturing improvements as countermeasures to inks already existing have been implemented with respect to this bronze phenomenon (cf. Japanese Patent Laid-Open No. 6-228476, Japanese Patent Laid-Open No. 7-247452, Japanese Patent Laid-Open No. 7-268261, Japanese Patent Laid-Open No. 2002-69340). However, actually there are almost no cases in which only ink with complete suppression of the bronze phenomenon has been applied. This is because of the limitations in the ink application range due to various factors such as an affinity with the discharge characteristics of the printing head causing discharge of the ink or an affinity with the printing medium and ink manufacturing costs.
As explained in FIG. 23, there are instances in which, depending on the type of ink, the bronze color is perceived as being different. Consequently, in regions in which numerous types of inks are mixed and expressed, there are instances in which different bronze colors are perceived. For example, when expressing specific color gamuts using inks with different bronze colors (colors of the regular reflected light), it is easy to perceive the differences in the bronze colors in the vicinity of the sections in which the combination of the inks used changes. At this time, when the bronze hues on both sides are close, no noticeable sense of incongruity is produced in the above-mentioned changed sections but when the bronze hues on both sides are largely different, a sense of incongruity is produced because of the differences in the bronze color in the above-mentioned changed sections. A sense of incongruity from the differences in the bronze color in these changes sections is perceived visibly as “bronze unevenness”.
FIG. 25A shows a conventional example in which the cyan-black hues using cyan ink and black ink are expressed. In FIG. 23 the bronze color of the cyan ink is tinged with red and the bronze hue of the second black ink is tinged with yellow. Consequently, in components in which cyan ink is predominantly used, the bronze is red and in parts in which the cyan ink is reduced and become a single black ink color, the bronze abruptly switches from red to yellow. Therefore, when the color region in the vicinity of this transformation reappears, “uneven color” due to the differences in the bronze colors is created and generally even when the perceived “uneven color” of the ink coloration itself is suppressed, a negative image effect is triggered which gives a sense of incongruity to those with a fine eye for color.